Data gathering system

ABSTRACT

A device for gathering data has first and second electrodes. The first electrode is coupled to a surface of interest, and the second electrode is coupled to “everything else” or “the air”. The first electrode is shielded from the second, and from most sources of parasitic capacitance, by a shield that is driven by an active driver that drives the shield to track, and ideally to match, the instantaneous potential of the electrode. The second electrode is likewise shielded in a similar way from most sources of parasitic capacitance. These shields likewise help to limit the extent to which RFI from the device electronics couples with either of the electrodes. In this way the sensing device achieves a markedly better signal-to-noise ratio at frequency bands of interest.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/377,339, filed Dec. 9, 2011 and entitled “DATA GATHERING SYSTEM,”which application is a 371 application of PCT/US2011/023013, filed Jan.28, 2011 and claims priority pursuant to 35 U.S.C. §119 to U.S.application Ser. No. 61/300,435 filed Feb. 1, 2010, and entitled“TWO-WRIST DATA-GATHERING SYSTEM” and to United States applicationnumber 61/378,878 filed Aug. 31, 2010, and entitled “DATA GATHERINGSYSTEM”. Each of the foregoing is incorporated by reference in itsentirety.

INTRODUCTION

Some electromagnetic communications, e.g., EKG signals, conductancecommunications, RF signals, etc., are very, very difficult to detect andgather, except with inconvenient or awkward data-gathering systems. Thegeneral ambient conditions can contribute noise in whichever portion ofthe EM spectrum is being investigated. The source of the desired EMsignal (for example a device within a live subject) may be overwhelmedor nearly overwhelmed by naturally occurring signals in the subject. Thedata-gathering device will likely contain a microcontroller and otherelectronics that will emit signals that further degrade thesignal-to-noise ratio for the data gathering.

Perhaps more subtly, but also very importantly, parasitic capacitances,however small in absolute terms, can suck away electromagnetic energy atthe frequency band of interest. Sources of parasitic capacitance caninclude relative positions of pairs of sensing electrodes, relativeposition of any single electrode relative to circuit boards containingground planes, and the relative position of any single electroderelative to large metallic or conductive bodies such as batteries orpower cells.

One example of a device within a live subject that may transmit a signalof interest is the ingestible event marker (“IEM”) described in U.S.Pat. No. 8,858,432, entitled “INGESTIBLE EVENT MARKER SYSTEMS”, U.S.Pat. No. 7,978,064, entitled “COMMUNICATION SYSTEM WITH PARTIAL POWERSOURCE”, U.S. Pat. No. 8,932,221, entitled “IN-BODY DEVICE HAVING AMULTI-DIRECTIONAL TRANSMITTER”, U.S. Pat. No. 8,258,962, entitled“MULTI-MODE COMMUNICATION INGESTIBLE EVENT MARKERS AND SYSTEMS, ANDMETHODS OF USING SAME”, US patent publication number 20090135886entitled “TRANSBODY COMMUNICATION SYSTEMS EMPLOYING COMMUNICATIONSCHANNELS”, U.S. Pat. No. 8,961,412, entitled “IN-BODY DEVICE WITHVIRTUAL DIPOLE SIGNAL AMPLIFICATION”, and U.S. Pat. No. 8,114,021,entitled “BODY-ASSOCIATED RECEIVER AND METHOD”, each of which isincorporated herein by reference.

Such an IEM is necessarily extremely limited in the amount of electricalpower available, and in the size of antenna available to couple thetransmitter to nearby transmission media. The emitted signal is thus notmuch stronger than typical ambient noise sources. Heretofore thedetection of such IEM signals has required the use of a patch, the patchhaving a form factor not unlike a large adhesive bandage, the patchapplied to the abdomen of a subject so as to be nearby to the IEM whenit emits its signal. The patch has potential drawbacks, among them therisk of irritation to the epidermis due to the adhesive attachment,possible interference with freedom of movement, and perhapsaesthetically displeasing appearance to some eyes.

An example of a data-gathering system that might be attempted is shownin FIG. 2. In such a system 201, the goal is to pick up a signaldetectable as between (a) a surface 102 such as tissue of a subject, and(b) the “air” or general ambient region (located everywhere else in FIG.2 besides the tissue and the detecting system). The pickup of signals isaccomplished by electrode 203, which is coupled to the surface 102, andelectrode 204, which is coupled to the “air”. Circuit board 208 carriescircuitry 207 and is connected with battery or cell (“battery”) 209. Thecircuitry 207 is connected to the electrodes 203, 204. The hope is thata differential amplifier in the electronics 207 could take as its inputeach of the two electrodes 203, 204 and thereby detect signals ofinterest. The system 201 might be dry-coupled to tissue (asdistinguished from the adhesive patch just described) and might beconveniently located elsewhere than the abdomen, for example in abracelet or wristband, if only under such circumstances it proved to bepossible to successfully detect the signals of interest.

Experience shows, however, that at frequencies of interest (perhaps tensof kilohertz), the parasitic capacitances present in such a device 201cause a loss of a large portion of any detected signal. The parasiticcapacitances may be conveniently modeled as being present betweenelectrode 204 and the ground plane of circuit board 208, betweenelectrode 204 and battery 209, between electrode 203 and the groundplane of circuit board 208, and between electrode 203 and battery 209.Some parasitic capacitance likely develops as well between the electrode203 and the electrode 204.

Experience also shows that RFI (radio frequency interference) is likelyto be emitted by the electronics 207 and then picked up by theelectrodes 203, 204. The desirably small form factor of a device 201will obviate the use of traditional ferrite chokes and the like thatmight otherwise be used to try to choke off some of the coupling pathsfor RFI. The small form factor also juxtaposes the electrodes and theRFI sources with very little physical separation.

One approach sometimes employed to attempt to reduce RFI is to “can” thesource of the RFI. In a device 201 this might be done by putting a metalshroud of a suitably selected metal or alloy around the circuitry 207.While this approach may indeed reduce RFI, it has the drawback ofintroducing still greater parasitic capacitances as between electrodes203, 204.

It would be very desirable if a way could be found to detect such faintelectrical signals reliably, in ways that would be more consistentlyacceptable to the subject than prior-art approaches. If a way could befound, it might be less irritating to the epidermis, might interfereless or not at all with freedom of movement, and might be moreaesthetically pleasing to some eyes.

SUMMARY

A device for gathering data has first and second electrodes. The firstelectrode is coupled to a surface of interest, and the second electrodeis coupled to “everything else” or “the air”. The first electrode isshielded from the second, and from most sources of parasiticcapacitance, by a shield that is driven by an active driver that drivesthe shield to track, and ideally to match, the instantaneous potentialof the electrode. The second electrode is likewise shielded in a similarway from most sources of parasitic capacitance. These shields likewisehelp to limit the extent to which RFI from the device electronicscouples with either of the electrodes. In this way the sensing deviceachieves a markedly better signal-to-noise ratio at frequency bands ofinterest.

DESCRIPTION OF THE DRAWING

FIG. 1 shows a sensing device according to the invention incross-sectional view;

FIG. 2 shows a possible sensing device according to the prior art incross-sectional view; and

FIG. 3 shows the sensing device of FIG. 1 in functional block diagramportrayal.

DETAILED DESCRIPTION

Turning to FIG. 1, what is shown is a sensing device 101 according tothe invention in cross-sectional view. The sensing device has first andsecond electrodes 103 and 104. The first electrode 103 is coupled to asurface of interest 102, which might be tissue of a living subject, andthe second electrode 104 is coupled to “everything else” or “the air”.Although it is largely a matter of semantics, one might choose tocharacterize the second electrode 104 as an electrode coupling to“ground” or “space ground”.

The first electrode 103 is shielded from the second electrode 104, andfrom most sources of parasitic capacitance, by a shield 105 that isdriven by an active driver (omitted for clarity in FIG. 1) that drivesthe shield 105 to track, and ideally to match, the instantaneouspotential of the electrode 103. The second electrode 104 is likewiseshielded in a similar way from most sources of parasitic capacitance bya shield 106. These shields 105, 106 likewise help to limit the extentto which RFI from the device electronics 107 couples with either of theelectrodes 103, 104. In this way the sensing device 101 achieves amarkedly better signal-to-noise ratio at frequency bands of interest ascompared with prior-art sensing devices.

Were it not for the shielding effects of shields 105, 106, theelectrodes 103, 104 would capacitively couple parasitically with thebattery 109, with ground planes in the circuit board 108, and with eachother.

FIG. 3 shows the sensing device 101 of FIG. 1 in functional blockdiagram portrayal. Electrode/shield assembly 104/106 plugs via connector301 to the circuit board 108. Electrode/shield assembly 103/105 likewiseplugs via connector 302 to the circuit board 108. The signal detected atelectrode 104 is amplified in amplifier 304, which drives shield 106.The signal detected at electrode 103 is amplified in amplifier 306,which drives shield 105. The signal detected at electrode 104 is alsoamplified in amplifier 303, providing one of two inputs to differentialamplifier 307. The signal detected at electrode 103 is also amplified inamplifier 305, providing the other of two inputs to differentialamplifier 307. The resulting signal (a difference between theinstantaneous potentials at the two electrodes) can then be filtered bya bandpass filter 308 and converted to a digital signal byanalog-to-digital converter 309.

It will be appreciated that the amplifier 304 will need to be selectedto have a frequency response sufficient to drive shield 106 at thefrequency band of interest and preferably at some higher frequencies.The amplifier 304 will also need to be selected to have enough power topump sufficient charge into and out of the shield 106 taking intoaccount its physical size and impedance. The same may be said ofamplifier 306 relative to its respective shield 105.

In an exemplary aspect the frequency band of interest is 54 kilohertzplus or minus five kilohertz. Thus bandpass filter 308 is chosen to passthis band. It is thought, however, that some IEMs could be developedthat emit signals at a megahertz or higher, in which case the datacollection device 101 would desirably carry out its function at suchfrequency bands. Other devices 101 could use a frequency band at about20 kilohertz.

It will be appreciated that amplifiers 303, 305, and 307, and filter308, and A/D converter 309 each need to have frequency responsesufficient for the frequency band of interest. It will be furtherappreciated that although the circuitry of FIG. 3 is depicted withdiscrete components such as individual op amps 303, 304, 305, 306, 307and discrete-component active filter 308, the benefits of the inventioncould just as well be gained by substituting a digital signal processorof sufficient frequency response for some or most of the componentsportrayed in FIG. 3, without departing in any way from the invention.The amplifiers 304, 306 need to have high gain at the frequencies ofinterest and need to have low noise.

In the present proof-of-concept aspect, a microcontroller (omitted forclarity in FIG. 3) receives signals which are stored as data in themicrocontroller (or in memory attached to the microcontroller), and thedata can then be communicated external to the device 101, for example toa general-purpose computer executing appropriate software for analysisof the received signals. The circuitry 107 is powered by a small“button” cell or battery. Another approach would be to communicate thedata wirelessly, for example via Bluetooth, to equipment external to thedevice 101. Such equipment may be a smart mobile phone running asuitable application to receive data via Bluetooth and to transmit thedata further to a remote host, via GPRS or other mobile-phone dataprotocol.

In the present proof-of-concept aspect, the device 101 is a flat squaredevice, 3 centimeters square. It is able to provide a wearablewristwatch form factor, only slightly larger than the button cell beingused to power the device 101.

The desirable result is to pick up the signals of interest from a singledistal point such as a wrist. The coupling would be by means of anon-sticky dry electrode with capacitive coupling to the body, or insome cases with electrically conductive coupling to the body. From auser's point of view this might be an elastic belt around the waist orchest, or an elastic wristlet band, or a necklace form factor.

The electrode 103 may be gold, or platinum, or stainless steel.

The active shielding accomplished with shields 105, 106 driven bydrivers 304, 306 permits the device 101 to pick up signals such as IEMsignals despite being further away from the IEM than the prior-artadhesive-bandage type of patch, and despite being non-sticky. This makesthe system of device and IEM more acceptable to users.

Further shielding may be disposed around the circuitry 107, connectedfor example to a ground plane within the circuit board 108, or connectedfor example to a potential defined to be between the rails defined bythe battery.

It will be appreciated that devices 101 could be used in pairs, eachtouching a body at a different place. The two devices 101 are eachcoupled with “space ground” and are thus to some extent coupled to eachother, through the electrodes 104. The paired devices could then collectdata from the body in a somewhat “dipole” receiver arrangement.

Those skilled in the art will have no difficulty devising myriad obviousvariants and improvements of the aspects set forth here, withoutdeparting in any way from the invention, all of which obvious variantsand improvements are intended to be encompassed by the claims whichfollow.

1. Apparatus for gathering data, the apparatus comprising: a firstelectrode, the electrode characterized as non-sticky, the electrodedisposed for capacitive or electrically conductive coupling with asurface; a second electrode, the electrode characterized as non-sticky,the electrode disposed for capacitive or electrically conductivecoupling with a region opposed to the surface; electronic circuitrydisposed between the first and second electrodes; the first electrodeshielded by a shield located between the first electrode and theelectronic circuitry; the second electrode shielded by a shield locatedbetween the second electrode and the electronic circuitry; theelectronic circuitry comprising a first driver and a first amplifierreceiving as an input a signal present at the first electrode, the firstdriver having an output coupled with the shield of the first electrode;the electronic circuitry comprising a second driver and a secondamplifier receiving as an input a signal present at the secondelectrode, the second driver having an output coupled with the shield ofthe second electrode; the electronic circuitry further comprising adifferential amplifier having first and second inputs, the first andsecond inputs connected to outputs of the first and second amplifiers,respectively; the differential amplifier having an output; theelectronic circuitry further comprising means for communicating dataindicative of the output of the differential amplifier to equipmentexternal to the apparatus.
 2. The apparatus of claim 1 wherein the firstelectrode and the second electrode are substantially planar and areparallel with each other, the electronic circuitry lying between thefirst and second electrodes and parallel thereto.
 3. The apparatus ofclaim 1 wherein the means for communicating data indicative of theoutput of the differential amplifier to equipment external to theapparatus comprises a connector providing a serial data path.
 4. Theapparatus of claim 1 wherein the means for communicating data indicativeof the output of the differential amplifier to equipment external to theapparatus comprises a Bluetooth link.
 5. The apparatus of claim 1wherein the output of the differential amplifier is bandpass filtered toa band including 54 kilohertz.
 6. The apparatus of claim 1 characterizedas unpowered from outside of the apparatus.
 7. The apparatus of claim 1further comprising a shield surrounding the electronic circuitry.
 8. Amethod for use in detecting signals, the method comprising the steps of:providing a first electrode, the electrode characterized as non-sticky,the electrode capacitively or electrically conductively with a surface;providing a second electrode, the electrode characterized as non-sticky,the electrode capacitively coupled with a region opposed to the surface;providing an electroninc circuitry between the first electrode and thesecond electrode; providing a first shield between the first electrodeand the electronic circuitry; providing a second shield between thesecond electrode and the electronic circuitry; driving the first shieldto follow a signal present at the first electrode; driving the secondshield to follow a signal present at the second electrode; deriving adifference between the signal present at the first electrode and thesignal present at the second electrode; and communicating dataindicative of the difference to equipment external to the apparatus,wherein the electronic circuitry comprises a first driver and a firstamplifier receiving as an input a signal present at the first electrode,the first driver having an output coupled with the shield of the firstelectrode, the electronic circuitry comprises a second driver and asecond amplifier receiving as an input a signal present at the secondelectrode, the second driver having an output coupled with the shield ofthe second electrode, the electronic circuitry further comprises adifferential amplifier having first and second inputs, the first andsecond inputs connected to outputs of the first and second amplifiers,respectively, and the differential amplifier has an output indicatingthe difference.
 9. The method of claim 8 wherein the communicating dataindicative of the difference to equipment external to the apparatuscomprises passing serial data through a connector providing a serialdata path.
 10. The method of claim 8 wherein the communicating dataindicative of the difference to equipment external to the apparatuscomprises passing data through a Bluetooth link.
 11. The method of claim8 wherein the surface is skin.
 12. The method of claim 11 wherein theskin is at a wrist.